1. Field of the Invention
This invention relates to a method of laser welding a single strand or a multistrand metallic conductor wire to a fixture.
2. Description of the Prior Art
In order to insure electrical and mechanical continuity metallic electrical conductors are attached to a thermal fixture by a variety of known welding techniques.
U.S. Pat. Nos. 3,524,963 (Swengel); 3,539,762 and 3,656,092 (both to Swengel et al.) disclose arrangements for arc welding a single metallic electrical conductor or a group of conductors to a generally cylindrical fixture. The metallic conductor(s) is (are) introduced into the cylindrical fixture and circumferentially surrounded thereby. In practice, a welding electrode is brought to bear into direct physical contact against the facial end of the conductor. As the electrode is displaced in a direction substantially coaxially with the axis of the portion of the conductor received in the fixture an electrical discharge is created between the electrode and the fixture whereby the same are fused together. The welding electrode may also be displaced in a direction approximately forty-five degrees to the axis of the conductor to initiate the discharge.
Arc welding is believed disadvantageous because of its practical requirement of direct physical contact between the electrode and the conductor being welded. This requirement is believed to contribute to inconsistencies in weld quality from weld to weld.
Other known welding techniques utilize a beam of welding energy, such as that produced by a laser of an electron beam source. The energy geam is directed toward the conductor wire and the terminal to form a molten pool of material. An example of this technique is disclosed in U.S. Pat. No. 3,610,874 (Gagliano). In this arrangement the beam of welding energy is directed primarily toward the terminal with a fringe of the beam being incident on the conductor wire. The beam is directed radially with resepct to the wire. The molten pool of material flows into the conductor/terminal interface. As the material cools the joint is formed therebetween.
This technique is believed disadvantageous due to the stringent control that must be exercised over the permissible magnitude range for the welding beam energy. The beam energy must be sufficient to melt the material of the terminal so it may form a pool which flows into the conductor/terminal interface. This threshold defines the lower limit of permissible beam energy. The upper limit of permissible beam energy must be less than that which would cause the conductor wire or the terminal to vaporize. It is recognized that the resultant weld joint should be stress relieved. Residual stresses could result in cracking of the joint.
An alternative laser welding technique is disclosed in copending application Ser. No. 4,197, filed Jan. 16, 1987, assigned to the assignee of the present invention. This application discloses an arrangement wherein the beam of welding energy is directed toward the terminal, whick generally overlies the conductor wire. The beam is directed radially of the conductor. A portion of the molten pool is unconstrained and is thus free to shrink as it solidifies without cracks being formed. Since the terminal shields the conductor wire the magnitude of lower energy level of the range of permissible beam welding energies is relatively high as compared to the method last discussed. This is due to the fact that it is necessary to melt completely through the terminal and partially through the conductor before the molten pool of material is formed. Also, the presence of the conductor beneath the terminal is believed to act as a heat sink. The upper limit of the range of permissible energies must be controlled to prevent the conductor from being vaporized.
U.S. Pat. No. 4,252,397 (Eigenbrode et al.), assigned to the assignee of the present invention, discloses another laser welding technique. In accordance with this patent an interconnection is formed using laser welding between a metallic conductor wire, in either single strand or multiple strand form, and a fixture in the form of the tines of an IDC (insulation displacement contact) terminal. The tines of such a terminal form a substantially open-mouthed, generally U-shaped slot. In accordance with the disclosure of this patent the insulation of the cable is removed and the metallic conductor wire strand or strands, as the case may be, are bent upon themselves to form a bight which loops over the insulation displacement contact terminal. FIG. 1 shows the resultant orientation of the metallic conductor wire (shown only as a single strand) and the terminal. Thereafter, the metallic conductor wire is rigidly attached to the terminal by directing a beam of laser energy from a position axially forward of the terminal toward the tips of the tines. A molten pool of material from the tines flows onto the conductor to form the joint.
Since the beam of welding energy is directed toward the surfaces of the tines of the fixture relatively close control must also be exercised over the magnitude of the energy beam. The patent is explicit in its teaching that laser welding energy must be maintained between ten and fifteen joules in order to form a weld without vaporizing the tines of the metallic fixture.
Accordingly, in view of the foregoing, it is believed advantageous to provide an arrangement for rigidly interconnecting, preferably by laser welding, the metallic conductor wire (in either single strand or multiple strand form) to a suitable fixture which requires less stringent control over the range of permissible welding energies.